1. Field of the Invention
The present invention relates to a chemical vapor deposition apparatus for use in manufacturing a semiconductor device. More particularly, the present invention relates to a gas analyzing apparatus for analyzing the residual gas in the reaction chamber of a chemical vapor deposition apparatus.
2. Description of the Related Art
A semiconductor device is generally manufactured by selectively and repeatedly subjecting a wafer to a number of processes such as photolithography, etching, diffusion, chemical vapor deposition, ion implantation and metal deposition processes. The etching, diffusion and chemical vapor deposition processes are performed by supplying a process gas into a sealed process chamber, and by providing an atmosphere in the chamber that facilitates a reaction between the process gas and the wafer. Accordingly, a gaseous by-product of the reaction, as well as unreacted/process gas, remain in the chamber as so-called residual gas at the end of the above-mentioned processes.
FIG. 1 illustrates a chemical vapor deposition apparatus for use in manufacturing a semiconductor device according to the prior art. The apparatus is provided with a residual gas analyzing apparatus for analyzing the residual gas in the process chamber.
Referring to FIG. 1, the process chamber 10 comprises an external tube 14 and an internal tube 16. Various kinds of processes, such as a plasma process, a diffusion process, or a chemical vapor deposition process, can be performed in the process chamber 10. A loadlock chamber 12 is disposed beneath the process chamber. A boat 18 accommodating several wafers to be processed is adapted to be driven by an elevator 20 upward and downward between the process chamber 10 and the loadlock chamber 12. A gas supply line 22 is connected to a bottom portion of the internal tube 16 of the process chamber 10 for supplying process or cleaning gas into the chamber. A valve 32 is installed in the gas supply line 22 for controlling the flow of gas through the gas supply line 22. Also, an SiH4 supply source 24, a PH3 supply source 26, an N2 supply source 28 and a CIF3 supply source 30 are connected to the gas supply line 22 via respective valves 32, 34, 36, 38, 40. On the other hand, waste gas left in the chamber 10 after the wafers are processed is exhausted through an exhaust pipe 42 using an exhaust pump 44. The waste gas is cleaned by a scrubber 46.
The chemical vapor deposition apparatus also has a system for analyzing the gas generated in the process chamber 10. The gas analyzing system includes a sampling port 48 connected to the external tube 14, and a sampling manifold 50 to which the sampling port 48 is connected by a flexible connector 52. A sampling pipe 54 of the sampling manifold is made of stainless material, has a ⅜ inch diameter, and is electro-polished. A first air valve 62, a second air valve 66, a first isolation valve 68, a second isolation valve 70, a third isolation valve 72 and a gate valve 74, are disposed in series along the sampling pipe 54. The first and second isolation valves 68, 70 each have an orifice of 100 microns in diameter, and the third isolation valve 72 has an orifice of 250 microns in diameter.
An N2 supply source 56 is connected in the sampling manifold 50 to supply N2 as a purge gas even while the sampling is not performed. A bifurcation 58 connects the N2 supply source 56 to both the first air valve 62 and the second air valve 66. A CM gauge 76 is installed between the first isolation valve 68 and the second isolation valve 70. A line 78 diverges from the sampling pipe 54 at the location of the CM gauge 76, and is connected to the scrubber 46 via a sampling pump 90.
The downstream end of the sampling pipe 54, in which the gate valve 74 is disposed, is connected to a residual gas analyzer 80. The residual gas analyzer 80 is an RGA-QMS (Residual Gas Analyzer-Quadrupole Mass Spectrometer) comprising an ion detector made up of an a mass spectrometer 84 provided with an ion gauge 82. The mass spectrometer 84 is connected to the scrubber 46 through a turbo pump 86 and a baking pump 88. The CIF3 gas from source 30 is used for cleaning polysilicon, silicon nitride, silicon glass and tungsten silicide, and can do so even in a low temperature state as opposed to while being in a plasma state. In particular, due to its extreme chemical selectivity, the CIF3 gas can be used to etch portions of the wafer that can not be reached by plasma. The CIF3 gas also has an advantage that it hardly generates any particles on the surface of the wafer.
When the apparatus is used to carry out an etch process, the lower the pressure in the process chamber, the more uniform the layer of material etched within the process chamber becomes. On the other hand, the process chamber 10 is preferably heated to a temperature greater than 400° C. to facilitate a satisfactory etching rate. This temperature is greater than that of the boiling point of CIF3. The CIF3 gas has a very strong reactivity and if the etching speed is too high, the tube itself is etched, whereby its thickness is reduced and its useful life is shortened. For this reason, the pipe for supplying the CIF3 is made of nickel, monel, Hastelloy, stainless steel 316L or a polymer. Furthermore, condensation may occur and thus damage the vacuum system of the apparatus. Therefore, a control for the purge cycle or cleaning time is very important.
Meanwhile, a sample of the gas under use or remaining in the process chamber is ionized by the RGA-QMS by colliding the gas with electrons accelerated by an electric potential difference of 70 eV. A mass spectrum is obtained of the ions having a specific mass-to-charge ratio, as discriminated according to the magnitude of their voltage. The composition of the ions obtained in this way yields desired information of the gas present in the chamber 10. The RGA-MS is a movable system in the form of a CIS (Closed Ion Source) in which the ions exist under a differential vacuum, as opposed to an OIS (Open Ion Source) of the type that is generally employed by sputtering equipment. Accordingly, the RGA-MS can analyze a process gas in addition to bulk gas.
Also, the residual gas analyzer 80 of the chemical vapor deposition apparatus includes a heater 92 for the ion detector. The performance of that part of the ion detector fit contacted by the gas from the process chamber 10 can be degraded by impurities in the gas. Heating the ion detector, e.g., the gas inlet of the mass spectrometer, overcomes this problem. FIG. 2 illustrates a conventional residual gas analyzer that includes such a heater.
Referring to FIG. 2, the RGA 80 is provided with a heater 92 comprising a filament and a heating jacket. A power switch 94 is connected to the heater 92 and to a power source for selectively providing and cutting off the supply of power to the heater 92. The power switch 94 is operated by a technician.
The power source is used to operate the process chamber 10, e.g., to supply power to a heater of the process chamber 10, whereby a baking process is performed. A technician manipulates the power switch 94 after power is supplied by the power source to the process chamber 10.
However, the heater 92 can thus be turned on or off by the technician regardless of whether the process chamber 10 is being heated using the power from the power source. Thus, if the technician does not switch the power switch 94 on/off at an appropriate time, defects can be produced in the wafers that are being processed.